The invention relates to a fountain or dampening duct for a dampening unit of an offset printing machine, the fountain having an inlet for dampening solution or medium, a return for the dampening solution, a base, at least one side wall, and a dam formed with an upper edge that is lower than an upper edge formed on the side wall.
A fountain of the foregoing general type is disclosed by Published European Patent Application EP 0 947 319 A1. The fountain described therein has an inlet for a dampening solution or medium, a return for the dampening solution, a base, side walls and a dam, an upper edge of which is lower than an upper edge of the side wall. This fountain is part of a dampening unit which is generally used in offset printing machines, in particular rotary offset printing machines, for applying the dampening solution to a printing form before ink is fed to the printing form. For this purpose, the dampening unit is also provided with a dampening roller, which is arranged at least approximately horizontally above the fountain and dips with a lower part of the circumferential surface thereof into dampening solution provided in the fountain and, as the dampening roller rotates, it transfers the dampening solution into the dampening unit and ultimately to the printing form. The dampening solution adheres to the hydrophilic areas of the printing form, which are defined by the image to be printed that is on the printing form. Moreover, the hydrophobic ink is applied to the printing form and adheres to the hydrophobic areas of the printing form, which are not covered by the dampening solution. In this manner, an inked image is produced on the printing form and, if necessary or desirable, after transfer from the printing form to a rubber blanket cylinder, is transferred to a printing material, for example, a paper web, cardboard or pasteboard, polymer material or the like.
In the case of the heretofore known dampening-solution fountain, the dam extends parallel to the longitudinal axis of the dampening roller. The inlet is provided at the bottom, close to the side wall opposite the dam. Because the upper edge of the dam is lower than the upper edge of the side walls, the dampening-solution level in the fountain is defined thereby. The dampening solution is directed continuously through the inlet into the fountain with the aid of a circulating pump, and the dampening solution running over the upper edge of the dam flows into a collecting channel provided with the return, and is guided back through the return to the circulating pump.
A dampening-solution fountain of the type mentioned at the introduction hereto is also disclosed by the Published German Utility Model DE 295 03 535 U1, corresponding to U.S. Pat. No. 5,870,952. In this fountain, the inlet is formed by a tube which, at the bottom, close to the side wall opposite the dam, extends over the entire length of the side wall and is formed with numerous small openings which are distributed over the entire length thereof.
In both of the foregoing heretoforeknown dampening-solution fountains, the flow of the dampening solution into the fountain is not uniform, i.e., neither in the case of the inlet being at a single point according to the Published European Patent Application EP 0 947 319 A1 nor in the case of the inlet being at numerous locations according to the Published German Utility Model DE 295 03 535 U1, corresponding to U.S. Pat. No. 5,870,952. As a result, a constant temperature distribution over the entire length of the fountain cannot be ensured. In addition, the heretoforeknown fountains have a rectangular outline, so that stagnation points necessarily occur. At these stagnation points, contaminants accumulate which originate from the environment of the printing machine and, for example, comprise small balls of ink which are produced in the inking unit. This accumulation of contaminants in the fountain rapidly becomes significant, and contaminates all of the dampening solution in the fountain. As a result, depending upon the composition of the dampening solution, the chemical stability of the dampening solution can be destroyed. Because a constant quality of the dampening and, accordingly, of the dampening solution is indispensable for optimum printing quality, it is necessary to empty and clean the dampening-solution fountain often in order to maintain the printing quality.
It is accordingly an object of the invention to provide a fountain for a dampening unit of a printing machine, which permits a longer service interval, i.e., in particular, requires less frequent emptying and cleaning, than heretofore known fountains of this general type.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a fountain for a dampening unit of an offset printing machine, comprising a container having an inlet for dampening solution and a return for the dampening solution, the container being formed with a base, at least one side wall connected to the base and a dam disposed on the base, the dam being formed with an upper edge that is lower than an upper edge formed on the one side wall, and further comprising a dividing wall having a run-off edge and an infeed edge, the dividing wall being seated on the upper edge of the dam and, starting from the dam, extending over the base to as far as the infeed edge, the infeed edge serving to define the level of the dampening solution in the fountain.
In accordance with another feature of the invention, the dividing wall has an upper side curved concavely with respect to the longitudinal axis of the fountain.
In accordance with a further feature of the invention, the radius of curvature of the concavely curved upper side of the dividing wall is constant, at least in sections.
In accordance with an added feature of the invention, the radius of curvature is greater than the radius of a dampening roller of the dampening unit.
In accordance with an additional feature of the invention, the infeed edge and the run-off edge of the dividing wall are at the same height.
In accordance with yet another feature of the invention, the infeed edge is higher than the run-off edge.
In accordance with yet a further feature of the invention, the dividing wall has an upper side that is flat, at least in sections, and is inclined at least approximately parallel to the longitudinal axis of the fountain so that the infeed edge is higher than the run-off edge.
In accordance with yet an added feature of the invention, the inlet is provided on the base adjacent to the dam.
In accordance with a concomitant feature of the invention, the fountain further comprises a collecting channel running beneath the run-off edge of the dividing wall and provided with the return.
Thus, the dampening-solution fountain according to the invention is provided with a dividing wall or partition having a run-off edge and an infeed edge, the dividing wall being seated on the upper edge of the dam and, starting from the latter, extending over the base to as far as the infeed edge, the infeed edge serving to define the level of the dampening solution.
Because the dividing wall is seated on the dam, the dampening solution can no longer run over the upper edge thereof, as in heretofore known fountains, but over the infeed edge of the dividing wall. From there, it is distributed on the upper side of the dividing wall, and flows at the run-off edge to the return. It is thus possible to produce a flow of the dampening solution at least approximately parallel to the circumferential surface of the dampening roller, at least in some sections. In this regard, the dampening roller is arranged above the dividing wall in a manner that a lower part of the circumferential surface thereof is wetted by the dampening solution at the upper side of the dividing wall.
In addition, the dividing wall serves as a cover, because contaminants falling down onto the fountain tend to land on the upper side thereof and are continuously flushed away by the dampening solution flowing on the upper side thereof towards the discharge edge. It is therefore no longer possible for downwardly dropping contaminants to accumulate in the dampening-solution fountain. Provision can be made for the upper side of the dividing wall to be curved concavely with respect to the longitudinal axis of the fountain, at least in some sections. The dividing wall therefore forms a channel extending at least approximately parallel to and under the dampening roller of the dampening unit.
In this case, provision can be made for the radius of curvature to be greater than the radius of the dampening roller. Provision can then preferably be made for the circumferential surface of the dampening roller of the dampening unit and the dividing wall to form concentric circular sections, at least in some sections.
In this case, provision can additionally be made, in a first alternative, for the infeed edge and the run-off edge to be at least at approximately the same height. Although the infeed edge and the run-off edge are at least at approximately the same height, the dampening solution nevertheless flows away over the run-off edge, because dampening solution is introduced continuously through the inlet into the fountain and flows over the infeed edge onto the upper side of the dividing wall. The desired flow of the dampening solution from the infeed edge towards the run-off edge can be assisted, in this first alternative, by having the dampening roller rotating in a manner that the lower part of the circumferential surface thereof moves from the infeed edge towards the run-off edge.
In this case, provision can additionally be made, in a second alternative, for the infeed edge to be higher than the run-off edge. Here, the desired flow of the dampening solution from the infeed edge towards the run-off edge is already achieved by the difference in height between these two edges. The dampening roller can then also rotate without difficulty in such a manner that the lower part of the circumferential surface thereof moves from the run-off edge towards the infeed edge.
The fountain according to the invention permits the time interval between maintenance operations to be longer than for conventional fountains, because, due to an encapsulation of part of the dampening solution in the fountain according to the invention, the latter is protected against contaminants and, due to the flow of dampening solution at least approximately parallel to the circumferential surface of the dampening roller, contaminants can be transported away over the run-off edge. Emptying and cleaning is therefore less frequently required.
Furthermore, in the dampening-solution fountain according to the invention, provision can be made for the upper side of the dividing wall to be flat, at least in some sections, and to be inclined at least approximately parallel to the longitudinal axis of the fountain in a manner that the infeed edge is higher than the run-off edge.
Furthermore, provision can be made for the inlet to be provided at the bottom of the fountain adjacent to the dam. Because the inlet is located far removed from the infeed edge, any flows which arise in the vicinity of the inlet as a result of the introduction of the dampening solution do not disrupt the flow of the dampening solution rising towards the infeed edge, so that the dampening solution can flow quietly and uniformly over the infeed edge. Provision can additionally be made for a collecting channel to run underneath the run-off edge of the dividing wall, and for the collecting channel to be provided with the return.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fountain for a dampening unit of an offset printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.